The present invention relates to an optical disc device and, more particularly, to an optical disc device for writing and reading data to and from an optical disc at a constant linear velocity.
A so-called image filing system as a business machine for recording and reproducing document data has been widely used. As known, in this system, image data is optically read out of an image bearing document, and the read out image data is recorded into the recording medium. In use, the image data as once recorded is read out from the recording medium, and reproduced by a display unit for visual presentation or a printer for hard copy.
The optical disc device employs an optical disc for recording image data. The optical disc spirally records the image data on the surface. For recording or reading out the image data, an optical head, set close to the optical disc, is driven by a linear motor to rectilinearly move in the radial direction of the optical disc.
Two systems for the record/read out of the image data have been known; one is a so-called constant linear velocity (CLV system), and the other is a so-called constant angular velocity (CAV system) In the CLV system, in order that the track on the optical disc moves at a constant speed relative to the optical head as moved thereto, the optical disc is rotated at such a rotating speed as is slower as the optical head moves from the inner side, i.e., the center portion, to the outer side, i.e., the peripheral portion of the optical disc. In the CAV system, the rotating speed of the optical disc is set at a constant value for stabilizing the record/read out operation and reducing an access time.
In the CLV system, for recording and reading out image data, the rotating speed of the optical disc is changed with a position of the optical head on the radial path above the optical disc. Therefore, it takes a long time until the rotating speed is settled down at a constant value. In this respect, the CLV system has a limit in increasing the rotating speed. Thus, the CLV system requires a long access time and a slow data transfer speed.
The CAV system inevitably rejects a high density record of data.